Image processing methods for improving the sharpness of an image by modifying edges in the image are disclosed in the Patent Documents listed below. In the image processing method disclosed in Patent Document 1, when the number of pixels of an input image is converted, a control value generated according to the high frequency components of the image signal is used to control the interpolation phase in the interpolation filter used for changing the number of pixels. Such control of the interpolation phase according to high frequency components produces sharper transitions at edges in the image, resulting in a crisper image.
The image processing method disclosed in Patent Document 2 enlarges an image, and then enhances edges by an amount responsive to the zoom ratio. This enhancement of the edges in an image after enlargement of the image prevents a reduction in edge sharpness due to the enlargement.
Patent Document 1: Japanese Patent Application Publication No. 2000-101870 (p. 3, FIG. 1)
Patent Document 2: Japanese Patent Application Publication No. 2000-137469 (p. 3, FIG. 1)